The invention pertains to a device for alternate admission of a liquid or a gas under pressure to one or more molds used in plastics processing.
Molds for plastics processing, such as injection molds, blow molds or extrusion dies, must generally be kept at a certain temperature, which in the injection and blow molding processes also effects a cooling of the plasticated compound introduced into the mold, and thus its solidification so that the molded part can be removed as quickly as possible from the mold. The temperature must be high enough so that the plastic will fill the mold completely and not "freeze" before the mold is completely filled. In extrusion processes the extrusion die generally has to be heated sufficiently so that the extrusion product with a perfect surface can be drawn off continuously and cooled in a cooling bath. In order to be able to utilize the very expensive plastics processing machines as effectively as possible, another requirement is the ability to replace molds as quickly as possible, so as to have the shortest possible downtimes for the machines when setting it up for a different injection or blow molding part or a different extrusion section.
It is known for this purpose to use quick-acting couplers as the connections to the molds. These known couplers can be easily released and are designed so that when the coupler is released no fluid can be discharged from the lines and the molds themselves.
Since the molds are generally cooled with water, occasionally water will remain inside the cavities of the molds over a longer period of time. This retained water can cause corrosion in these cavities. Furthermore, such quick-acting couplers are expensive and susceptible to malfunctioning so that simple quick-acting couplers which do not automatically close when detached are preferred. The use of such simple couplers causes fluid to drain out of the mold when the coupler is detached, which in turn may cause soiling and corrosion on the outside of the molds and in the mold cavities, the latter being far more critical.
It is also important, in order to achieve high utilization rates for the machines, that the molds be quickly brought up to the desired temperature.